System of control for electrical devices



LIL/m92.

Jan. 9, 1923.

1. H. HUNT. y SYSTEM 0F CONTROL FOR ELECTRICAL DEVICES.

FILED MAR. 27. 1919.

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SYSTEM OF CONTROL FOR ELECTRICAL DEVICES.

FILED MAR.27.1919. 2 SHEETSSHEET 2.

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application nea nach ai', rara. man nu earner.

Be it lrnown that l, JOHN citizen ot the United States of America,residing at Dayton, lcounty of Montgomery, vState ot Uhio, have inventedcertain newv and useful improvements in Systems of Control torElectrical, Devices, of which the following is a full, clear, and exactdescri tion. l .Y l

T is invention relates to systems of control tor electrically operateddevices, such as for example, devices lfor heating Water tor domesticpurposes.

@ne of the objects ot the inventionis'to provide manual means forrendering such a device, operative when desired, and to provideautomatic means tor rendering it in operative in case of tailuremanually to render it inoperative. vlli/'here the invention is appliedto an electrically operated 'water heater, one` manner of carrying outthis ob- 'ject consists in providing a plurality ot manually operablecontrolling devices which may be vplaced in separate rooms, and each .otwhich will control vthe operation ot the heater; and inproviding anautomatic controller operated by a thermostat for turning oil' theheater when the water or other fluid has reached a predeterminedtemperature. rllvhus, it the operator should fail to turn ott' theheater after using a quantity of hot water, the heater would beautomatically turned ott'. This automatic controller is so constructedand the system of control is so arranged that, after the automaticcontroller has operated to turn od the heater, each ot the manuallcontrolling devices will be left in acondition whereby they may beoperated to turn on the burner again without manipulation ot theautomatic controller.

4 @ther and turther objects and advantages ot the present invention willbe apparent from the following description, reference being had to theaccompanying drawings, wherein a preterred embodiment of the presentinvention is clearly shown.

f ln the drawings:

'Fig l is an elevational view of a water system including the presentinvention, the water heater being4 shown in section, and together with awiring diagram ot the electric circuits included in the system.

-Fig. 2 is a side elevation of the automatic switch, certain parts beingshown in section.

lll. Hour, a -i lFig. 3 is a sectional'vievv talren on line 3,3 ot' Fig.2.. 'l -v v Fig. t is asectional view taken on line fil-,4t of Fig. 2. vlln the drawings, a liquid tuel burner' 20, including an air receivingchamber 21 and a combustion chamber 22, is 'connected with water packet2t.' rlhe water or other liquid to 'be heated enters jaclret 2t throughpipe -25 and is conducted out through pipe 26 to a .conduit systemhaving taucets 27 and 28. Air tor combustion and 't'uel atomizingpurposes is furnished by a `tan blower 30 which is driven by a motor 3l.Air under pressure conducted trom blower 30 to air receiving 'chamber2l, a portion ot this air entering the combustion chamber 22 throughythe slits' 32 torln'ed in the wall ot' the comfa lire tube 23' aroundwhich isplaced a through a pipe 34 extending down into a quantity oitber 36. j v

Fuel is elevated :trom fuel chamber 36 to the atomizing level incombustion chamber 22 by means ot air pressure. A portion ot air in thechamber 2l is conducted to the tuel chamber through a passage 37 whichis adjusted by screw 38. 'lhe chamber is also iuel 35 located in thetuel champrovided with a bleeder orifice 39 which cooperates withpassage '37 to obtain the desired reduction of air pressure in thechamber 36. rll`he particular function of these orifices is described inmy co-pend'ing application, erialhlo.' 285,662 filed Marci 27,1919.

rlFhe ignition ot the fuel is accomplished through the agency ot a..spark` plug l() connected with ignition coil secondary winding 4l.

ignition coil primary winding t2 is connected with stationary contact 43which operates with a vibrator all. Vibrator at is connected Vwith wire45 which also connects motor brush li6 with the battery 50. Motor brusht7 is connected with motor ield winding 48 which is connected vby wiret9 with certain of the controlling devices to be described. Primarywinding 42 is also connected with wire 49.

A three-Way switch 5l is provided with a switch arm 52 connected withwire 4:9.

Arm 52 may cooperate with contact 53 with a rack 90. Rackr which isconnected by wire 55' with automatic switch contact 56, or'with switchcontact 54 which is connected by wlre 57 with switch 59 includes switcharm 60 which is connectedV by wire 61 ,with a movable contact 62mounted'upon/a pivotally mounted arm 63 but insulated(y therefrom.Contact.

62 cooperates with a contact 64 which is connected by wire 65 withbattery 50. Arm' 60 may cooperate with stationary contact 66 connectedby wire 67 with an automatic switch contact 68, or with stationarycontact 70 connected by wire; 71 withI automatic switch contact 72.

Switch contacts 68, 56, 72 and 58 Vare arrangedr to be connected inopposite palrs by switch blades 73 and 74 which are mounted upon 'plate75 insulated therefrom and from each other. Plate 75- is looselyjournalled u on shaft 76 which turns in a bearing 77 ormed in l thebase-78 of the automatic switch and in a bearing 79 formed in the switchcover 80. Shaft 76 carries ratchet wheel 81 with which cooperates aratchet pawl 82 ivotally mounted upon a pawl plate 83 which is looselyjournalled upon 83 is provided with a which engages wlth rack shaft 76.Plate gear segment 84 85 provided with atooth-portion 86 engaglng gearsegment 87. Segment 87 is pivotally mounted at 88 and carries a pinionsegment 89 meshing its lower end with a -sylphon bellows 91 which ismounted withinl a cup" 92 adapted to hold a quantity of ether .orsimilar substance which eipands readily under the acother liquid in thetion of heat.

up 92is mounted so as to come in direct contact with the water orjacket24 and is provided with a cover 93. A spring'94 interposed between.the bellows and the cover 93 tends to resist the movement of the rack 90 due to the action of heat.

Thevratchet wheel 81 is connected with the switch `blade plate 75 bymeans of a spring 100 which tends to produce relative movement between'said ratchet vand said plate. In order to prevent this movement atcertain times the plate 75 carries a stud 101 upon which is pivotallymounted a-latch 102. Latch 102 is provided with a finger 103 whichextends beyond the plane of latch 102 and projects over the edge of asta`A tionary latch plate 104 which is mounted upon the base 78. Inorder that the latch 102 may be released by turning shaft 76, said shaft76 is provided with an eccentric 105 which is located within anelongated hole 106 formed in said latch plate l102. It is apparent thatby turning shaft76 in a clockwise direction that the latch 102 will I.be swung free of the latch plate 104 and will .permit the plate 7 5 tomove 90". Whenthis 58. A three-way (see Fig. 4) but 90 is connected atvcarried by lever 63.

The operation of the invention is as follows: y

p Assuming that the switch arms 52 and 60 are in the positions shown inFig. 1, current will. flow from the battery y50 to the motor through thefollowing circuit: battery 50, wire 45, brush 46, brush 47, series field48, wire 49, switch arm 52, contact 53, wire 55, Contact 56, blade 73,contact 68, wire 67, contact 66, arm 60, wire 61, contact 62, contact64, wire to battery 50. When this circuit has been completed the motor31 will operate the blower 30 causing fuel to be elevated from chamber36 from the atomizing lever and the combustion' chamber 32 where saidfuel is blown out toward the tube 23 in the form ofA aspray and mixedwith combustion air entering the passages 32. Current for fuel ignitionpurposes 1s supplied from battery 50 through the following circuit: wire45, vibrator 44, contact 43, primary winding 42, wire 49 to wire 65through the connections just described, and thence to bat` tery 50. Thevaction of the vibrator 44 in interrupting the primary circuit will causea shower of sparks to occur at the spark plug 40. Fuel will be ignitedand willburn in a long' flameextending some distance into the. tube 23.The walls of the tube will be quickly heated and will transmit heat tothe water or other Huid in the acket'24.

ot water may then be drawn off from either of the faucets 27 or 28.

The switches 51 and 59 are located conveniently near the faucets 28 and27, re-

which is well known. It is to be understood that.,switch arms 52 and 60will occupy either the positions shown in full lines iii Fig. 1, or thedotted line positions 52"l and 60a, respectively, wherein said contactarms 52 and 60 will engage contacts 54 and 70 respectively.

If the operator should forget to turn off the blower in the mannerdescribed, the

p blower will be turned off automatically by `and assuming that switches52 and 60 have manana -the operation of which will now be de.-

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scribed. lnitially, -the temperature of the water in the heater is at orbelow a certain temperature which will be known as normal temperature.`The bellows 91 and parts connected therewith will occupy the positionshown in Fig. 1. Allt a certain' predeter mined temperature of thewater,which -shall be known as the intermediate temperature, the ether orother liquid contained within -the cup 921will have expanded to such anamount as to cause the to move npwardly'and to impart through members69,v 87,' 86 Aand 65, sufficient clockwise rotation to -pawl arm ,83 tocause the Aratchet 81 to move sufliciently to effect the release oflatch 102.. When this predetermined :intermediate temperal ture has beenreached, the plate 75 will be rotated 90 causing the blades 73 and 74 tobe moved into positions 7 3u and 7 4-, respectively, as shown in Fig".4. Contacts 56, 72, 56 and 68 will then be bridged. lll/'ith switch.blades 7 3 and 74 at 73a' and 74, respectively,

been left in the full line position, shown in lFig. 1, the circuit fromthe batter to the mot-or and -ignition apparatus will e interrupted. ltis to be observed, however, that the circuit connections have beenrearranged by the automatic switch so that all'y that is necessary tostart the heater is to turn either of the switches52or 60 into thepositions 52 or 60a, respectively. For example, lif blades 73 and 74 arein positions y73a moving switcharm 52 into position 52a where it is inengagement with contact 54. 'lhe circuit from the battery to the motorwill then be as follows: battery 50, wire 45, brush 46, brush 47, motorfield 48, wire 49,-arm

l 52a, contact 54, wire 57, contact 58, blade 74, contact 68, wire 67,contact `66, switch arm 60, wire 61, contact 62, contact 64, wire 65 andbattery 50. Assuming that switch blades 73 and 74 are in the positionsreferred to, and that switch arm 52 remains in engagement with contact53, by moving contact 60 into position 60a where itl willy lengagecontact 70, the following circuit between the motor and the battery willbe established: battery 50, wire 45, brush 46, brush 47, motor field 48,wire 49, switch arm 52, contact 53, wire 55, contact 56, blade` 73a,contact 7 2,- wire 71, contact 70, switch arm 60a, wire 61, contact 62,contact 64, wire 65, and battery 50..

rlhus it is apparent that means have been provided .for controlling` theheater at a plurality of locations, and that in case the heater is notshut oil' manually, the heating will be stopped automatically upon theattainment of a l predetermined intermediate temperatureof the liquid tobe hea-ted. vllurl thermcre this automatic device does not 'infor hotwater will bemadeibefore the water wai-ll have cooled od sufciently forthe thermostatically controlledelements to return to the normalpositions shown in Fig. 1. lf after such further dem-and the operatorshould carelessly leave the circuit connections closed between thebattery and motor,

it is obvious that a considerably higher perature of the water wouldneed to be at tained before sufficient motion could beim* parted to theswitch shaft 76' to open the blower circuit. ln order to yprevent thetemperature of the water reaching a value which would be excessive,vfurthermeans are provided for opening the circuit between the batteryand the motor upon the attainment of a predetermined maximum temperatureof the water. llfhen this device operates the manually controlledswitches will be rendered ineffective to start the burner again untilthe operator has been put to the inconvenience of restoring theautomatic' switch toits normal position. This inconvenience to which theoperator is put will serve as a reminder in the future not to forget toturn olf the burner by means of the manual switches. Thisresult isaccomplished in the'. following manner:

rl`he relation of levers 63 and 111 and the spring 113 is such that whenthe predetermined intermediate temperature of the water is reached, suchas to effect the throwing of such blades .73 and 74 in the mannerdescribed, the arm 111 will be moved upwardly but not sufficiently tocause the axis of spring 113 to move above the pivot 63a. But as thetemperature of the water exceeds the predeL termined intermediate value,the rack B5 will continue to move upwardly and finally cause the axis ofspring 113 to move above the pivot 63a, when a predetermined maxi mumtemperature is reached. v'lhis will cause the arm 63 to move upwardlyagainst stud 120 and to interrupt the circuit by sepa-l rating thecontacts 62 and 64. rlhe circuit between the battery motor and ignitionapparatus is now interrupted in such a fashion that the switches 51 and59 are inoperative to close the circuit. 'lhe burner will cease tooperate 'and the temperature of the water will decrease untilv the lever111 returns to the position shown in lFig. 1.

iso

The lever 63, however, willjbelheld against result from the Waterbecoming too hot, and the inconvenience to the operator ensuingl fromthe necessity of restoring the lever 63 to normal position may act as areminder to the operator to manually turn off the burner when not inuse.

However, it kmay be desired in every instanceto turn off the burnerautomatically andlat the same time arrange the electrical circuits sothat manual control can loe effected without any resettingoperation. Toaccomplish this result the stud 120 is located at 120B, (see Fig. 1).termined maximum temperature is reached, the lever. 111 will have movedupwardly to bring the axis of spring 113 above the pivot 63a. causinglever 63 to move upwardly to break the circuit land shut off the burner.The thermostat will cool ofi` causing the movable elements associatedtherewith to return to their normal positions, shown in Fig. 1. In thisform of thev invention the spring 113 will' restore lever 63automatically to circuit closing position whereupon the burnerl willoperate for a short period to heat the thermostat to the intermediatetemperature whereupon the switch shaft 76 will be moved sufficiently toeffect the opening of the circuit' in the manner described. Thisautomatic control protects the-heatin system since opportunity forcooling ofi'I t e burner and liquid container is afforded during thelapse of time necessary for thel spring 113 to lbe restored to normalposition.

Where a plurality of three-way switches are employed to effect theremote control of the burner, a signal device is provided for indicatingwhether or not the burner is already in operation. Switches 51 and 59are provided with lamps 151 and 159, respectively, which are connectedin series by wire 153, and in shuntwith the motor and ignition coilbywires 152 and 154. Whenever from the battery the lamps 151 and 159will burn. `.Therefore, for exam-` ple, if the same one desiring toobtain water from faucet'Q/ has turned on the burnerl by means of switch59, any one desiring to obtain water from faucet 28 will knowbyobserving the lighted lamp 1.51 that the burner is already on and thatit 1s not necessary to operate the switch 51. Where faucets and switchesare located at such a distance from the burner that its operation is notaudible, if such signal device were not provided, confusion would resultas one'operator might visions; of manual Now when the prede-4 turecontrolled 'turn off the burneriwhileanother would be cient tryingtoobtain'a supply of-hot water.

-While the form of mechanism herein shown and described constitutes apreferred form of' embodiment ofthe invention, it is to be understoodthat other forms might be adopted, all coming within the scope of theclaims which follow.

I claim: y 1. 'In a system of control for electrically operated heaters,the combination with a heater having electrical operating proelectricalprovisions operative; and automatic temperature controlled means forrendering said electrical provisions inoperative,said automaticmeans'being ineffective means for rendering the to renderlsaidprovisions operative until rendered operative again by said manuallmeans. M

2.- In a system of control for electrically operated heaters,thecombination with a heater having electrical operating provisions; ofa plurality of manual devices each operable to render the electricalpro- Visions operative; and automatic temperameans for rendering saidelectrical provisions inoperative, said automaticA means beingineffective to render said provisions operative until rendered operativeagain by either of said manual devices.

3. In a system of control for electrically operated heaters, thecombinationI with a heater having electrical operating provisions; of alplurality of manual devices eachoperable to render the electricalprovisions operative; and automatic means operable' at a certaintemperature for rendering said electrical provisions inoperative, saldautomatic means being ineffective to render said provisions operativeuntil rendered o erative again by either of said manual evices, saidautomatic means being operable at a predetermined higher temperature torender said provisions inoperative and'said manual devices ineffectivefurther to render said provisions o erative.

4. In a system of control or electrically operated heaters, thecombination with a heater having electrical operating provisions; ofmanual electrical provisions operative; and automatic means operable ata' certain temperature for renderingsaid electrical provisionsinoperative, said automatic means being ineffective to render saidprovisions operative until rendered operative again by sald manualmeans, said automatic means being operable at a redetermined'highertemperature `to render said provisions inoperative and said manual meansineffective further to render said provisions operative.

5. In a system of control for electricallyl pump and ignition devicesfor said burner;\\

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latina i l a battery; manual means for connecting the battery 'with themotor `and ignition devices; and automatic temperature controlled meansfor disconnecting said battery, said means being ineHective toconnectthe same again until connected by saidmanual means.

tl. ln a system of control for electrically operated heaters, thecombination with a liquid fuel burner, a motor y operated air v pump andignition devices for said burner;

a battery; of a plurality of manualiswitches each operable to connect'the batte-ry with the'motor and ignition devices; and auto matictemperature controlled means forv disconnecting said battery, said meansbeing inell'ectiveto connect the same a ain-until connected by either ofsaid manua switches.

7. ln a system of control for electrically operated heaters,v thecombination with, av liquid fuel burner, a motor operated air pump andignition devices for said burner;

, a battery; ot a plurality of vmanual switches each operable -toconnectthe battery with the motor `and ignition devices; and aut-omatic meansoperable at a certain temperature for disconnecting said battery andineffective to connect the same again until with a burner and a fluidcontainer; of detill titi

connected by either of said manualswitches, said automatic means beingoperable at a predetermined higher temperature to disconnect the batteryand ytol render said switches inent'ective to connect the battery withthe motor and ignition devices.

8. ln a system of control for electrically operated heaters, thecombination with a liquid fuel burner, a motor operated air pump'andignition devices for said burner; a battery; manual means for connectingthe battery with the motor and ignition devices; and automatic meansoperable at a"certain temperature for disconnecting said battery andineffective to connect the same again until connected vagain bysaidmanual means, said automatic means being operable at a predeterminedhigher temperature to disconnect the battery and to render said manualmeans ineffective to connect the battery with the motor and ignitiondevices. 9. ln a heating system, the combination vices for manuallycontrolling the burner; and temperature controlled means forautomatically turning oft' the burner while permitting said manualdevices further to control said burner; and means for indicating thestatus of the burner at each of said manual devices.

10. ln ,a heating system, the combination with a liquid fuel burner, amotor operated air pump and ignition devices for 'thev lo irner; of abattery; 'a plurality of manu-` al y operated switches each for'connecting the battery with said motor and ignitionvdevices; andatemperature controlled switch ttl means including instrumentalitiesresponsive to temperature changes in the duid for lstopping the burner,saiddevice being movl able to'start the burner 'without a return of thesald instrumentalities to their initial position. l2.- lln a heatingsystem, the combination` with a liquid fuel burner, a motor operatedairs pump and ignition devices for the burner; of an electrical circuitincludin a battery; a plurality of manually opera le switches, each ofwhich is adapted to coniplete the circuit through thebattery, motor andignition device; 'and a temperature controlled switch for breaking thecircuit, any one of sald lswitches being operable then to complete thecircuit.

13. ln a heating system, the combination with a burner and a Huidcontainer heated thereby; of an electrical circuit controlling theburner and including a manually operable. switch having a plurality ofoperable posi-tions for completing the circuit; and an automaticmechanism responsive to temperature changes in the Huid for breaking theclrcuit and stopping the burner, the switch being operable then tocomplete the circuit.

la. ln a heating system,l the combination with a burner anda fluidcontainer heated thereby; of an electrical circuit controlling theburner 'and including a manually operable switch having a plurality ofoperable positions for completing the circuit; and an automaticmechanism responsive to temperature changes in the fluid for breakingthe l1@ circuit and stopping the burner, the switch being operable thento complete the circuit, said mechanism being operable at a relativelyhigh temperature of the fluid to again open the circuit and prevent astarting of the 115 burner by operation of the switch.

l5. ln a-control for ,electrically operated fluid heaters,instrumentalitiesI responsive to temperature changes in the fluid; andmeans operated by said instrumentalities and 120 'adapted to render-aheater inoperative at each of a plurality of predetermined temperaturesof the Huid.

' 16. ln an electrical control forburners,

the combination with a fluid chamber adapt- 125 switches whereby aIcircuit broken of said paths may be'completed `to 'be heated by circuit'controlling the burner E. changes in the chamber'landhaving ai plu-y-rallty of@ circuit closing positions; and ai plurality .ofi currentpaths between `said along another of the paths by operationv of themanually operable SWtC 17 g 4In an electrical control for burners, the

A. combination with a AHuid chamber adapted a burner; of an electricalyand' comprising'a manually operable switch having a 'if'. `plurality ofcircuit closing automatic rotary switch responsive to tem- .positions anperature changes in thejchamber 'and hav- .circuitl closing currentpaths pleted along another of the paths operation of the manuallyoperable switc `18.l In an electrical control for burners,thecombination with 'a fluid chamber adapted to be heated by a burner;'of an electrical circuit controlling the burner and compris-A v `ingaumanually l operable switch having a pluralityy having a plurality 'ofcircuit closing positions;

i along one of said vthe combination with a ed to. be heated by aburner.; of an electri-k `operation of the automatic switch and aplurality of current paths between said switches whereby a circuitbrokenpaths may bercompleted along another of the paths by operation 'of themanually operable switch.

19. In an electrical control for burners,

fluid chamber adaptcal circuit controlling the burner and comprising amanually operable switch having a plurality of circuit closingpositions; an automatic switch responsive to temperature changes in the'chamber and having a plurality of circuit closing positions; a plural'-ity of current paths whereby a circuit broken along one of said pathsmay be completed along another of the paths by operation of the manuallyoperable switch; and automatic means for breaking a circuit along any ofsaid paths. n

20.- In a heatin system, the-combination with a liquid fue burner, a.kfluid chamber heated thereby, and a single source of electricalcurrent; of an electrical circuit com-v prising a switch responsive totemperature changes in the fluid heated; a manually operable switch; andconnections between the switches, the burner and the source of currentwhereby an electrical circu-it broken by may be completed by operationof the manually operable switch'.

21. In a heatingv system, the combination with a liquid fuel burner, afluid chamber along one of circult closing positions; an 'automaticrotaryv switch responsive to tem. jperature changes in the chamber onlyduring increase in the temperature thereof and loperable switches, eachbetween said switches heated thereby,

vperature to breakthe circuit;

and the current source whereby an electrical circuit broken by operationofthe automatic -swit'ch may be completed by operation of any of saidmanually operable switches.

.22. Ina heatin system, the combination with a liquid fue burner, auidchamber heated thereby, yand a source of electrical a circuit breaking'switch responsive to tem-4 perature changes in the fluid heated; aplurality of manually-operable switches; and connections between thesame, the burner and the current source whereby an electrical A.circuitbroken by operation of one of said manually'. operable switches may becompleted y by' operation of another manually operable swltch.

23'. In a heating system the combination with a liquid fuel burner, afuel-chamber heated thereby, and a single source of electrical current;of a plurality of manually having a plurality of circuit closingpositions; an automatic rotary switch having successive operativepositions and res onsive to temperature c langes in the liquid heated'to .break a circuit made by any of said switches; and connectionsbetween the switches, the burner and the current source whereby acircuit broken by movement of the rotary switch to its next position maybe completed by operation of any of said manually operable switches. y'

24. In a system of control for electrically operated burners, thecombination with a burner, and a source of electrical current; of anelectrical circuit comprising two manually operable switches; and anautomatic temperature controlled switch connected in series between thetwo manually operable switches whereby after o eration of the automaticswitch to break t e circuit, either manually operable switch may bemoved to again complete the circuit.

25. Ina .heating system the combination with a liquid fuel burner, aiuid chamber and a source of electrical current; of an electricalcircuit comprising a -manually operable switch; temperature controlledcircuit breaking means operable at a moderate and at a relatively hightemand connections between the switch, circuit breaking means, theburner and the source of current whereby the circuit is automaticallybroken at a relatively lw temperature in the iiuid heated, may becompleted again by operation of themanuallytoperable switch without asubstantial lowering of the temcurrent; of an electrical circuitcomprisinL l igianea'e i' perature of the fluid, and will be brokenagain automatically upon an abnormal 1ncrease in temperature of theHuid.

'26. ll'n a heating system the combination with a liquid fuel burner, afluid chamber heated thereby, and a source of electricall current; of anelectrical circuit comprising circuit breakmg means responsive totemperature changes in the fluid heated to break `may bel made byoperation ot any of the switches and a circuit broken at the highertemperature cannot be made by operating said switches.

27. ln a heating system-the combination with a burner and a chamberheated thereby; of a source of current, an electrical cir 5 cuitcomprising two manually operable switches each having a plurality otcircuit closing positions; and a temperature controlled circuit breakingmechanism including two automatically operated temperature controlledswitches one of which is connected to the two switches by a plurality ofcurrent paths whereby ay circuit bro-ken by the said automatic switchmaybe completed by operation of a manually operable switch, and theother of said automatic switches beingoperableonly at high temperaturesin themedium heated to break the circuit and hold it open until thetemperature of the medium has decreased.

28. lln an electrically operated heater, current controlling vmeanscomprising an electricaly circuit; a manually operable switch having aplurality of operable positions fon completing the circuit; and acircuit con trolling device including instrumentalities responsive tochanges in temperature ot' the medium heated to break a circuit made bysaid switch in any one ot its operative positions and to reform thecircuit whereby it may be completed by said switch in another of itsoperative positions.

lln testimony whereof ll affix my signature.

Jl-lhl lil. HUNT.

Witnesses:

HAZEL SoLLnNBnRenn,

lidnummer)L Panna,

